This is taken from

Updated I January 2017

This is an attempt to
compare the cartridge destructiveness, gun power and gun efficiency of post-WW2
fighter guns. Fighter armament fits in three key periods are also considered.

Cartridge Destructiveness PART 1

In the similar analysis carried out for World War 2 fighter armament, it was noted that there are two types of energy that may be transmitted to the
target; kinetic and chemical. The kinetic energy is a function of the projectile
weight and the velocity with which it hits the target. This velocity in turn
depends on three factors: The muzzle velocity, the ballistic properties of the
projectile, and the distance to the target. There are therefore two fixed
elements in calculating the destructiveness of a projectile, its weight and
chemical (high explosive or incendiary) content, and one variable element, its
velocity. The key issue is the relationship between these three factors.

A high muzzle velocity will provide a short flight time,
which is advantageous in increasing the hit probability and extending the
effective range, and will also improve the penetration of AP rounds. However, it
might not add much to destructiveness, as unless an AP projectile hits armour
plate (and not much of the volume of an aircraft is protected by this), a higher
velocity just ensures that a neater hole is punched through the aircraft; the
extra kinetic energy is wasted. Also, if the projectile is primarily relying on
HE blast or incendiary effect, the velocity with which it strikes the target is
almost immaterial. Provided that it hits with sufficient force to penetrate the
skin and activate the fuze, the damage inflicted will remain constant. In
contrast, AP projectiles lose effectiveness with increasing distance.

It is sometimes argued that a projectile with a high muzzle
velocity and a good ballistic shape (which reduces the rate at which the initial
velocity is lost) provides a longer effective range. To some extent this is
true, but the greatest limitation on range in air fighting remains the
difficulty in hitting the target. The problem of hitting a target moving in
three dimensions from another also moving in three dimensions (and probably at a
different speed and on a different heading) requires a complex calculation of
range, heading and relative speed, while bearing in mind the flight time and
trajectory of the projectiles. Today, such a problem can easily be solved by a
ballistic computer linked to a radar or laser rangefinder, but in the early
years of this period the technical aids were far less sophisticated. And this
was without considering the effects of air turbulence, G-forces when
manoeuvring, and the stress of combat.

For all of these reasons muzzle energy (one half of the
projectile weight multiplied by the square of the velocity) has not been used to
calculate kinetic damage as this would overstate the importance of velocity.
Instead, momentum (projectile weight multiplied by muzzle velocity) has been
used as an estimate of the kinetic damage inflicted by the projectile. It might
be argued that even this overstates the importance of velocity in the case of
high-capacity HE shells, as noted above, but the effect of velocity in improving
hit probability is one measure of effectiveness which needs acknowledging, so it
is given equal weighting with projectile weight.

Chemical energy is generated by the high explosive or
incendiary material carried by all air-fighting projectiles. First, there is the
difference between HE and incendiary material, which are often mixed (in very
varying proportions) in the same shell. HE delivers instant destruction by blast
effect (plus possibly setting light to inflammable material within its blast
radius), incendiaries burn on their passage through the target, setting light to
anything inflammable they meet on the way. The relationship between the
effectiveness of HE and incendiary material is difficult to assess. Bearing in
mind that fire has been the big plane-killer, there appears to be no reason to
rate HE as more important, so they have been treated as equal.

The comparison between kinetic and chemical energy is the
most difficult and complicated subject to tackle. This complexity is revealed by
the example of a strike by a delay-fuzed HEI cannon projectile. This will first
inflict kinetic damage on the target as it penetrates the structure. Then it
will inflict chemical (blast) damage as the HE detonates. Thirdly, the shell
fragments sent flying by the explosion will inflict further kinetic damage (a
thin-walled shell will distribute lots of small fragments, a thick-walled shell
fewer but larger chunks), and finally the incendiary material distributed by the
explosion may cause further chemical (fire) damage.

There will therefore always be a degree of arbitrariness in
any attempt to compare kinetic and chemical energy, as it all depends on exactly
where the projectile strikes, the detail design of the projectile and its fuze,
and on the type of aircraft being attacked. To allow a simple comparison, we
will reduce all these factors to an increase in effectiveness directly
proportional to the chemical content of the projectile. We assign to projectiles
that rely exclusively on kinetic energy an effectiveness factor of 100%. For
projectiles with a chemical content, we increase this by the weight fraction of
explosive or incendiary material, times ten. This chosen ratio is based on a
study of many practical examples of gun and ammunition testing, and we will see
below that it at least approximately corresponds with the known results of
ammunition testing.

To illustrate how this works: a typical cannon shell consists
of 10% HE or incendiary material by weight. Multiplying this by ten gives a
chemical contribution of 100%, adding the kinetic contribution of 100% gives a
total of 200%. In other words, an HE/I shell of a given weight that contains 10%
chemicals will generate twice the destructiveness of a plain steel shot of the
same weight and velocity. If the shell is a high-capacity one with 20% chemical
content, it will be three times as destructive. If it only has 5% content, the
sum will be 150%, so it will be 50% more destructive, and so on.

The following table for the most common cartridges and
loadings used in aircraft guns shows the consequences of these assumptions and
calculations. The first few columns should be self-explanatory, as these are
basic statistics about the ammunition. The 'DAMAGE' column shows the results of
the calculations described above. To run through an example, let us look at the
case of the 30 x 113 B. The projectile weighs 270 g, (which equals 0.270 kg)
and is fired at 720 m/s. Multiplying these gives 0.270 x 720 = 194.4, so you
have a momentum factor of 194.4. As the bullet contains 17.2% by weight of
incendiary material, the momentum is multiplied by 2.72 to give a destructive
power score of 528.768 - rounded to 529.

'In the last
column – 'Power' – the 'Damage' result is divided by ten and rounded to the
nearest whole number (except for the 12.7 x 99) to simplify later calculations.

Table 1A: Cartridge
Destructiveness

(Figures in brackets are
estimates.)

CARTRIDGE

TYPE

ROUND WEIGHT

MV
(m/s)

PROJECTILE WEIGHT (g)

% HE/I

CONTENT

DAMAGE

POWER

12.7x99

API

112

890

43

2

46

4.6

20x102

HEI

263

1,030

101

11

218

22

20x110

HEI

257

830

129

8.8

201

20

20x110 USN

HEI

270

1,010

110

(11)

(233)

(23)

23x115

HEI

325

740

175

10.8

269

27

25x137

HEIT

492

1,100

184

16.7

540

54

27x145B

HEI

516

1,024

260

(15)

(666)

(67)

30x113B

HEI

500

720

270

17.2

529

53

30x150B

HEI

530

1,025

275

17.5

775

77

30x155B

HEI

840

790

400

12.1

695

69

30x165

HEI

830

860

390

12.4

751

75

30x173

HEI

890

1,080

360

15

972

97

37x155

HEI

1,300

690

729

6.7

840

84

Comments on Table 1

Clearly, the resulting scores can only be approximate, and in
particular will vary depending on the particular mix of types included in an
ammunition belt. The power calculation takes a typical mix of ammunition, where
known. They also take no account of the fact that some incendiary mixtures, and
some types of HE, are more effective than others. However, they do provide a
reasonable basis for comparison. There is no point in trying to be too precise,
as the random factors involved in the destructive effects were considerable.

Cartridge Destructiveness PART 2

The calculations concerning
cartridge destructiveness shown above are valid for the early decades
of the postwar period, but there is an argument that the importance of
HE content has declined since then, for two reasons. The first is that
the nature of the targets has changed: a typical modern fighter is a
much bigger and heavier beast than its 1950s equivalent and has little
empty volume inside (conversely, there are relatively few big bombers
left in service). A thin-walled, high-capacity Minengeschoss type of HE
projectile, as used very successfully in World War 2, would be of
little use as penetration to an effective depth would be unlikely. As a
result, modern HE shells are more strongly made, with the percentage HE
content reduced acordingly.

The second reason is that different types of projectile have been
introduced, partly in response to the change in target characteristics.
The most conventional of these are the SAPHEI rounds (base-fuzed, with
a thick steel full-calibre penetrator containing a reduced quantity of
HE) which are now the standard combat nature for both the 30x113B and
30x150B rounds made by Nexter of France for their revolver guns. In
parallel with this, other kinds of multipurpose rounds combining HE,
incendiary and armour penetrators have been developed, such as the
20x102 PGU-28 series in the USA (based on a Nammo design), and the new
25x137 APEX round, also from Nammo, which has a tungsten alloy
penetrator contained within the HEI shell. Finally, two modern types of
multipurpose projectile have no chemical content at all: the FAP
(Frangible Armour Piercing) initially made in 20x102 and 27x145B, and
PELE (Penetrator with Enhanced Lateral Effect), available in various
calibres. Both of these are designed to penetrate their targets before
breaking up into a lethal shower of fragments, said to deliver
destructive effects comparable with an HE shell.

Clearly, the method of calculating effectiveness described above
is no longer appropriate, as it would classify FAP and PELE as no
better than solid steel practice rounds. It is very difficult to say
how the modern, stronger HEI shells and SAPHEI, APEX, FAP and PELE
would all compare with each other in effectiveness; it would probably
depend upon the circumstances. There does not appear to be any
publicly-available evidence which would support favouring one
type of projectile over another. Accordingly, in the revised table for
modern cartridges shown below, the chemical contents have been ignored.
However, just omitting the percentage uplift given for chemical
contents would result in the ammunition becoming apparently less
effective than before, which is not the case: to try to provide a basis
for comparison with the earlier system, a standard percentage has
therefore been applied to all combat cartridges; around 15% seems
reasonable (i.e. multiplying the projectile weight by the MV, then
multipying by 2.5x and dividing by 1000). The results of this are shown
below:

Table 1B: Cartridge
Destructiveness (without chemicals)

CARTRIDGE

TYPE

ROUND WEIGHT

MV
(m/s)

PROJECTILE WEIGHT (g)

DAMAGE

POWER

20x102

HEI

263

1,030

101

260

26

23x115

HEI

325

740

175

323

32

25x137

HEIT

492

1,100

184

506

51

27x145B

HEI

516

1,024

260

666

67

30x113B

HEI

500

720

270

486

49

30x150B

HEI

530

1,025

275

705

70

30x165

HEI

830

860

390

838

84

30x173

HEI

890

1,080

360

972

97

Gun Power and Efficiency

The cartridge destructiveness table above only shows the
relative effect of one hit. When comparing the guns that fired the cartridges,
other factors come into play, namely the rate of fire (RoF) and the gun weight.

To calculate the destructive power of the gun, the 'POWER'
factor from the above table has been multiplied by the RoF, expressed in the
number of rounds fired per second. This gives the relative 'GUN POWER' figures
in the table below.

To judge how efficient the gun was, the 'GUN POWER' result is
divided by the weight of the gun in kilograms to provide the 'GUN EFFICIENCY'
score in the last column. This is, in effect, a measure of the power-to-weight
ratio of the gun and ammunition combination.

Table 2A: Gun Power and
Efficiency (EARLY)

GUN

CARTRIDGE

ROF
(rps)

CARTRIDGE POWER

GUN POWER

GUN WEIGHT

GUN EFFICIENCY

.50 M3

12.7x99

20

4.6

92

29

3.2

M39

20x102

27

22

594

81

7.3

M61A1

20x102

18-100*

22

792-2,200*

114

19.2*

M61A2

20x102

30-100*

22

1,320-2,200

93

14.2-23.7*

Hispano V

20x110

12.5

20

250

42

6.0

Mk 12

20x110 USN

18

(23)

(414)

46

(9.0)

NS-23

23x115

11.5

27

310

37

8.4

NR-23

23x115

15

27

405

39

10.4

GSh-23

23x115

54

27

1,460

50

29

GSh-6-23

23x115

150

27

4,050

76

53

GAU-12/U

25x137

13-70*

54

1,404-3,780*

123

11.4-30.7*

BK 27

27x145B

28

(67)

(1,876)

100

18.8

Aden/552

30x113B

22

53

1,170

87

13.4

30M554

30x113B

30

53

1,590

85

18.7

30M791

30x150B

42

77

3,234

120

26.9

NR-30

30x155B

15

69

1,035

66

15.7

GSh-301

30x165

27

75

2,025

45

45

GSh-30

30x165

50

75

3,750

105

35.7

KCA

30x173

22

97

2,134

136

15.7

N-37 /

NN-37

37x155

6.7 / 10.8

84

563 / 909

103

5.5 / 8.8

Table 2B: Gun Power and
Efficiency (LATE)

GUN

CARTRIDGE

ROF
(rps)

CARTRIDGE POWER

GUN POWER

GUN WEIGHT

GUN EFFICIENCY

M61A2

20x102

30-100*

26

1,560-2,600

93

16.7-28.0*

GSh-23

23x115

54

32

1,728

50

34.6

GSh-6-23

23x115

150

32

4,800

76

63

GAU-12/U

25x137

13-70*

51

1,326-3,570*

123

10.8-29.0*

GAU-22/A

25x137

10-55*

51

1,020-2,805*

104

9.8-27.0*

BK 27

27x145B

28

67

1,876

100

18.8

30M554

30x113B

30

49

1,470

85

17.3

30M791

30x150B

42

70

2,940

120

24.5

GSh-301

30x165

27

84

2,268

45

50.4

GSh-30

30x165

50

84

4,200

105

40.0

KCA

30x173

22

97

2,134

136

15.7

Comments on Table 2

* The figures for the power-driven rotaries are for the full
RoF. In practice, the figures in air combat will be lower because of the time
taken to accelerate. For example, the M61A1 only fires 18 rounds in the first
0.5 seconds, and 68 rounds in the first full second of firing. In the first
second, the gun power figure will be 1,496 and the efficiency 13.1. If only the
first half-second of firing is counted, then the (full-second equivalent)
figures become 792 for gun power and 6.9 for efficiency. The GAU-12/U has the
same spin-up time as the M61A1, 0.4 sec, so will be affected about as much by
this factor, with full-second scores of 2,592 and an efficiency of 21, and
half-second scores of 1404 and 11.4. The
spin-up time of the GAU-22/A, the new 4-barrel version of the GAU-12/U,
is not yet known so it has been taken as 0.4 s as well. The gas-powered GSh-6-23 and GSh-6-30 will
be affected far less, and spin-up time has been reduced to 0.25 sec for the
lighter M61A2 for the lighter M61A2, improving its scores accordingly.

Two factors not included are gun reliability and total
ammunition weight. The former is simply not available in most cases. The latter
involves too many variables. First, the ammunition supply for most guns varied
according to the installation. Furthermore, in searching for comparators, there
would be the problem of which measures to take: the weight of the number of
rounds fired per second, or the weight of the number required to inflict a
certain amount of damage? There would be a case for either of these, but they
would produce very different results. This issue is however addressed in the
next table.

Fighter Firepower

Finally, a consideration of how the firepower of fighters
compared with each other. The aircraft have been grouped in early postwar,
1954-1970, 1970-1990 and 1990+ fighters, and have been chosen to be
representative of their period.

Table 3: Fighter
Firepower

Name

Armament

Weight (kg)

Ammo
Power

Gun
Power

Time to fire
2320

1945-53

De Havilland Vampire

4 × Hispano Mk.V (150)

322

12000

1000

2.32

North American F-86A
Sabre

6 × Browning .50 M3 (267)

353

7370

552

4.20

Grumman F9F Panther

4 × Hispano M3 (190)

363

15200

1000

2.32

Yakovlev Yak-23

2 × NR-23 (60)

117

3240

810

2.86

Mikoyan-Gurevich MiG-15

1 × N-37D (40)
2 × NR-23 (80)

285

7680

1373

1.69

Saab J 29

4 × M/47C [HS.804] (180)

393

14400

1120

2.07

Hawker Hunter

4 × Aden (150)

648

31800

4680

0.50

1954-70

Mikoyan-Gurevich MiG-19S

3 × NR-30 (120)

500

24840

3105

0.75

North American F-100A

4 × M39 (275)

613

24200

2376

0.98

Vought F8U Crusader

4 × Mk.12 (144)

340

13248

1656

1.40

Lockheed F-104G

1 × M61A1 (725)

305

15950

2200

1.05-1.37

Saab J35A Draken

2 × m/55 [Aden] (90)

264

9540

2340

0.99

Mikoyan-Gurevich
MiG-21F-13

1 × NR-30 (30)

91

2070

1035

2.24

Northrop F-5A

2 × M39 (280)

309

12320

1188

1.95

Mikoyan-Gurevich
MiG-21PFM

1 × GSh-23L (200)

115

5400

1460

1.59

Dassault Mirage IIIC

2 × DEFA 552 (125)

299

13250

2340

0.99

BAC Lightning F.6

2 × Aden Mk.4 (130)

304

13780

2340

0.99

1970-1990

Grumman F-14 Tomcat

1 × M61A1 (767)

315

16874

2200

1.05-1.37

Northrop F-5E

2 × M39A2 (280)

309

12320

1188

1.95

Mikoyan-Gurevich MiG-23M

1 × GSh-23L (250)

131

6750

1460

1.59

Dassault Mirage F.1

2 × DEFA 553 (125)

299

13250

2340

0.99

General Dynamics F-16

1 × M61A1 (511)

248

11242

2200

1.05-1.37

Saab JA 37 Viggen

1 × KCA (150)

270

14550

2134

1.09

Mikoyan-Gurevich MiG-29

1 × GSh-301 (150)

170

11250

2025

1.15

Mirage 2000C

2 × DEFA 554 (125)

299

13250

2340

0.99

Tornado ADV

1 × BK 27 (180)

193

9900

1876

1.24

Sukhoi Su-27

1 × GSh-301 (150)

170

11250

2025

1.15

1990-

Saab JAS 39

1 × BK 27 (120)

162

8040

1876

1.24

Dassault Rafale

1 × GIAT 20M791 (125)

186

9625

3234

0.72

Eurofighter Typhoon

1 × BK 27 (150)

177

10050

1876

1.26

Lockheed-Martin F-22

1 × M61A2 (480)

219

10560

2640

1.05-1.25

Comments on Table 3

The armament installations are listed in the second column.
The specified weight is the weight of the bare guns and the ammunition. It does
not include belt links, ammunition tanks, gun mounting points and recoil
buffers, et cetera. The ammunition power value is the cartridge power value from
Table 1, multiplied by the number of cartridges carried. The gun power value is
the sum of the gun powers as in Table 2. The final column gives the time in
seconds, needed to fire the equivalent of an ammunition power of 2320. The
choice of this value is somewhat arbitrary; it was selected simply because the
heaviest armed WW2 fighter – the Me 262 – was capable of delivering this
firepower in one second, so it enables easy comparisons to be made. 'Two 'Time
to Fire' figures are given for the American rotaries; the slower time is from a
standing start, the faster one assumes that it is spinning at maximum rate
throughout.

The fighters are here divided into four groups. The first
group, which entered service in the late 1940s and early 1950s, was subsonic in
level flight and had guns as main armament. Most of these fighters carried an
improved form of WWII armament, with guns that were technically refined and had
a higher rate of fire. One fundamental change in comparison with WWII is that,
with the exception of the hugely successful MiG-15 (and the improved MiG-17) all
had homogenous armament. The practice of fitting multiple types of gun to a
fighter was abandoned by most nations.

In 1953 the Hawker Hunter entered service with an armament of
four Aden cannon. With a power rating of 4680, this is the most powerful gun
armament listed here. All later fighters carried substantially less cannon
firepower. Most air forces were satisfied with lighter gun armament than the
RAF, and the introduction of homing air-to-air missiles in service soon led to a
reduction of gun armament. Not listed here are the Gloster Javelin and the early
models of the BAC Lightning, which could carry four Aden cannon, or two Aden
cannon and missiles.

The next group, from the late 1950 to 1970, contains the
first supersonic and Mach 2+ fighters. In this time period many interceptor
fighters entered service without cannon armament. Although multi-role and air
superiority fighters often retained cannon, attempts to improve their firepower
were limited. Guns fell victim to weight reduction programmes, or were (as in
the case of the F-104 and Mirage III) installed as optional equipment packages.
The Lightning F.6 entered service as a missile-only fighter, but cannon were
retrofitted from 1970 onwards.

The third group, from 1970 to 1990, all had guns designed
into them, under influence of the US experience in Vietnam. Despite the
introduction of several new types of cannon, none of these fighters exceeds the
gun firepower of the Me 262 by a substantial margin – and the total weight of
the guns plus ammunition is only about 300 kg or less. The same figure for the
Me 262 was 413 kg, but one also has to consider that the ballistic performance
of modern fighter cannon is much superior and the performance of sighting
systems has been much improved. This allowed for some weight reduction; the
Soviet fighters clearly have the lightest gun installations.

Finally, the last group includes four fighters that are
currently entering service. Here we see again an improvement in firepower,
although the 30M791 and M61A2 are both direct descendants of older guns, rather
than innovative designs. On the other hand the destructive capacity of the
ammunition carried is decreasing again, to levels that are actually somewhat
inferior to the better armed of the WWII fighters. This is defended with the
argument that modern sighting systems are so accurate, that the hit probability
is far higher than the 2% typically achieved during WWII, when aiming was mostly
dependent on the skill of the pilot. Despite a reduced ammunition capacity and a
gun redesigned to reduce the weight, the installation of the F-22 remains heavy
in comparison with that of other fighters, without benefiting much in firepower.

For the smaller JSF, Lockheed Martin at first selected the BK 27
revolver, then changed to the GAU-12/U five-barrel rotary, then finally to a
four-barrel version of the GAU-12/U, designated GAU-22/A. This will only be
fitted internally in the Air Force F-35A version; the STOVL F-35B and naval
F-35C will have the option of carrying one in a gunpod under the rear fuselage.
The GAU-22/A's maximum RoF of 3,300 rpm delivers a gun power of 2,800. The
spin-up rate is not yet clear, but assuming it is the same as the GAU-12/U (0.4
secs), the gun power varies from about 1,000 (the half-second
standing-start rate) through 1,850 (the full-second standing
start). The length of time to reach the '2320 score' will be 1.17 seconds from a
standing start and 0.86 seconds at
maximum rate.